In recent years, in the field of Intelligent Transport System (ITS), research and development have been carried out on a technique that measures positional information of vehicles or pedestrians by using a stereo camera installed at an intersection or the like. The measured positional information is used for, for example, driving support for vehicles. In order to measure the positional information with high accuracy, the installation state of the stereo camera needs to be calculated with high accuracy, and a process of calculating the installation state of the stereo camera is referred to as “calibration.”
Calibration methods of the related art include a method (hereinafter, referred to as “the related art”) which is disclosed in Patent Literature (hereinafter, referred to as PTL) 1. In the related art, three-dimensional positions (x, y, and z) of three or more markers and two-dimensional positions (u and v) of each marker in an image are measured. Next, a rotation matrix T that converts a three-dimensional position into a two-dimensional position is obtained by using linear regression. The calculated rotation matrix T is expressed as a product of rotation matrixes around axes, and thus rotation angles (φ, θ, and ψ) around the axes are calculated. A rotation angle having a minimum difference S between the rotation matrix T and a rotation matrix T obtained by returning the calculated rotation angles to the product of the rotation matrixes is set to the installation state of the stereo camera.